Welding of helically formed tubing



Feb. 10, 1959 Filed NOV. 30, 1955 77 RADIO Fvcau c ANDREI- Gunman/r500w. c. RUDD 2,873,353

WELDING OF HELICALLY FORMED TUBING 2 Sheets-Sheet 1 HVVENTUR.

VI ZILLA CE C. R000. BY

Feb. 10, 1959 w. c. RUDD WELDING OF HELICALLY FORMED TUBING Filed Nov.30, 1955 2 Sheets-Sheet 2 INVENTOR.

MLLA CL C. Rune. BY

Mmwz

Patented Feb. 10, 19 59 dice WELDELJG F HELECALLY FORMED TUBING WallaceC. Rudd, Larchrnont, N. Y., assignor to Magnetic Heating orp., NewRochelle, N. Y., a corporation of New York Application "November 30,1955, Serial No. 549,986

6 Claims. (Cl. 219-62) This invention relates to methods and apparatusfor welding metal tubing of the type formed by helically winding a metalribbon while welding together adjacent edges of the ribbon along ahelical line. More particularly, the invention relates to a method andmeans for forming such weld by electrical resistance heating of theedges to be elded by the use of high frequency current.

Reference is made to the copending application of Wallace C. Rudd andRobert I. Stanton, Serial No. 421,768, filed April 8, 1954, and to theirpreceding application Serial No. 332,422, filed January 21, 1953 (nowabandoned), the subject matter of said applications being disclosed alsoin Belgian Patent No. 530,877, granted August 31, 1954. Saidapplications and said patent disclosed a method and means for weldingtogether the edges defining the longitudinal gap in metal tubing' as thetubing is advanced longitudinally while applying pressure thereto toclose said gap at a weld point. According to said method, the heating ofthe gap edges is effected by the use of electrodes connected toanoscillatory current source and applied respectively adjacent cientlyhigh so that the lowest impedance path between the electrodes followssaid gap edges to and from the weld point. The present inventioninvolves a novel ap- "1 paratus arrangement and a modification of themethod of said prior applications, such as to provide for the welding ofthe above-mentioned helically formed type of tubing.

Various further and more specific objects, features and advantages ofthe invention will appear from the description given below taken inconnection with the accornpanying drawings illustrating by way ofexample certain preferred forms of the invention.

In the drawings:

Fig. 1 is a perspective view illustrating one embodiment of the methodof the invention and the arrangement of the principal apparatus partsfor performing such method;

Fig. 2 is a sectional view taken substantially along line 22 of Fig. 1;

Fig. 3 is a somewhat schematic diagram of one form of apparatus forcarrying out the invention;

Fig. 4 is a view similar to Fig. 1 but illustrating an alternativemethod and arrangement; and

Fig. 5 is a sectional view taken substantially along line 5-S of Fig. 4.

Referring to Fig. 1 in further detail, a mandrel is provided as at itwhich may be rotatably supported by suitable bearing means indicated ata (Fig. 3) and arranged to be rotated about its axis at a constant speedin the direction indicated by the arrow 11 by a suitable ment and arewelded along a helical path, as indicated at 13. As the mandrel with theformed tube thereon rotates, the tubing as formed is also advanced (inthe general direction indicated by the arrow 14) and by the use ofsuitable known types of apparatus which per se form no part of thepresent invention.

The welding of the abutting gap edges takes place at a so-called weldpoint preferably at the region indicated at '15 in Fig. 1. At points onor adjacent the approaching edges of the metal strip which are to abutand at some distance in advance of the weld region, high frequencyelectrical current is applied to the edges respectively by contacts orelectrodes 16, 16a which slidably engage the metal of the strip at oradjacent its said edges. That is, as best shown in Fig. 2, theelectrodes, such as 16, 16a, may be mounted on and suitably secured tometal holders as at 17, 18 which are insulated with respect to eachother as by a suitable insulation piece 19 located therebetween. Whilesaid electrodes may be shaped and positioned to engage either the edgesurfaces per se of the metal strip or either the upper or the undersurface thereof near such edges, yet as shown in Fig. 2 the electrode 16is preferably so shaped and positioned at to engage the under surfacenear and at the edge of strip 12 whereas the electrode 16:: is shaped toengage at and near the outer or upper surface of the convolution 12',that is, at a point indicated at 29. The electrode holders as shown areconnected respectively to the two terminals of a source of oscillatorycurrent of high frequency, preferably radio frequency in the range of to500 kilocycles per second. With current of such frequencies, the path oflowest possible impedance connecting the electrodes 16 and 16a will bealong the approaching gap edges 21, 22 as indicated by small arrows inFig. 1, that is, from the electrodes to and from the weld region $5.This is for the reason that the conditions are such that with currentsof these frequencies the predominant impedance factor will compriseinductance and the path of lowest inductance will be along the closelyadjacent and approaching gap edges and thus the heating effect of suchcurrent will be closely confined to such edges. Suificient current isused thereby to cause resistance heating of such edges up to weldingtemperature. That is, from the points where the edges come into contactwith the electrodes, any given point on said edges will be heated moreand more until same reaches the maximum temperature just at thebeginning of the welding region where a noticeable arc will occur.

As above noted, the electrode 16 is preferably applied to the undersideof the edge of strip 12 and electrode 16a is applied to the upper orouter surface of convolution 12'. This insures that the current willtend to concentrate most along the lines which are close together on theedge regions approaching the weld and thus the current will be alonglines providing for the minimum reactance by reason of such closeness.

It should also be noted that the points on the bottom corner of edge 21will normally be the first to come in contact with edge 22 and will doso by contacting points on the top corner of edge 22. Thus with theelectrodes in the preferred positions above described, the points whichtend to be hottest will contact first, creating a small are which willinsure adequate heating of the remaining edge surfaces sufiiciently sothat the surface on edge 21 will wipe against the surface on edge 22 asthe edges come into the final desired abutting relationship.

The contact holders 17, 1.8 may be supported by any suitable insulationbrac set means not shown and the dis tance between the electrodes andthe weld may be determined and adjusted by trial so that with apredetermined set of conditions and with a given amount of current, theapproaching gap edges will have time to be heated up to weldingtemperature and not substantially higher at the moment when they firstcome together.

The mandrel 10, as best shown in Fig. 2, may be formed on its surfacewith an annular recessed portion or groove 23 at the region wherewelding occurs so that the edge of convolution 12' will be spaced apartfrom the metal pf'the mandrel thereby preventing the dissipation of heatfrom the edge 22 into the mandrel and preventing any tendency for aportion of the current to travel along the surface of the mandrel ratherthan as desired along the edge 22'of the convolution 12'. Nevertheless,under certain circumstances it may be found that more heat will berequired to heat the edge 22 (hereinafter referred to as the trailingedge of its convolution) up to welding temperature than in the case ofedge 21 (hereinafter referred to as the forward edge of ribbon 12) whichis spaced widely out of contact with the mandrel. On the other hand,under some circumstances the formed portion of the tubing may havebecome sufficiently heated so that less heating will be required foredge 22 than for edge 21. For instance, this might be so in the case ofquite thin tubing welded with closely spaced convolutions. Thus toaccommodate these conditions, the contact or electrode supports shouldbe positioned and adjusted by trial independently at suitable distancesfrom the weld point. That is to say, for example, if edge 21 requiresless heating, then electrode 15 would be placed closer to the weld or incase more heating of this edge is required, this electrode would bespaced further from the weld. The same is true as to the properpositioning of electrode 16a along edge 22.

As somewhat schematically indicated in Fig. 3, the strip 12 may beadvanced toward the mandrel by suitable pairs of pinch rollers at 25.The strip should be yieldably urged sideways to bring the edges 21, 22into firm contact for welding and this may be accomplished as by springpressed rollers somewhat schematically indicated at 26, 26' and anopposed guide roll being indicated at 27. At a suitable positionfollowing welding of the edges together, the strip may be pressedagainst the mandrel as by a pressure roller 28.

With the method and arrangement shown in Figs. 4 and 5, the same mandrelsupporting and rotating means therefor may be used as well as the samemeans for feeding the strip as shown in Figs. 1 and 3 except that inFig. 4, however, the strip is suitably fed in a position so that thetrailing edge 30 of formed convolution 31 will be overlapped by the edge32 of strip 33 so that such edges will be overlapped and welded togetherwith a cross-sectional formation as indicated in Fig. 5. Also with thearrangement as shown in Figs. 4 and 5, preferably just following theweld point, the overlapped edges are pressed firmly against the mandrelas by a pressure applying roller 34. Furthermore, with this arrangementthe annular gap in the mandrel is preferably omitted so that the weldwill be firmly supported by the mandrel in the region of the pressureroller 34.

The contacts or electrodes 35a, 36a for applying the current with thearrangement of Fig. 4 may be preferably adjustably supported the sameway as those of Fig. 1.

With the arrangement of Fig. 4, since the edge 30 will be in contactwith the mandrel to which some heat may be dissipated as well as some ofthe heating current, it will generally be necessary to provide a longerheating path for its edge 36 than for its edge 32 and consequentlyelectrode 36a should generally be adjusted at an appropriate distancefrom the weld point which will be greater than the distance of electrode35a from the weld point.

The method and arrangement of Fig. 4 may often be preferred to that ofFig. 1 inasmuch as the approaching edges will come together at agiven-point, viz., the point indicated at 35, and remain together atsuch point without relative movement thereby providing a more closelydefined weld point or, strictly speaking, a more closely defined weldline or small area. Furthermore, with the overlapping edges, as-in Fig.4, the problem of pressing and holding the welded surfaces together issimplified as compared with the method of pressing edges. in) abuttingrelation. Also with the arrangement of Fig. 4, it will be apparent thaton both the trailing edge 30 as well as on the forward edge 32 bands onthe opposed surfaces will be heated, that is, at the edge 30 the highfrequency current will travel along and be concentrated along a bandupon the upper (that is to say the outer) surface which faces and comesclosest to the edge 32, and at the edge 32 the high frequency currentwill be concentrated upon and cause heating of a band on the under orinner surface at that edge. The concentration of the heating on thesebands, of course, arises because of the effects of mutual inductancebetween the current flows on opposite sides of the gap. And it will beapparent that the width of these bands where the heating isconcentrated" will be determined by the extent to which the edgeportions overlap, even though the degree of overlap may vary. Thus theheating to welding temperature will be concentrated upon just theparticular surface portions which are to come into engagement and bewelded together regardless of the full surface width of the strips.Because of such concentration of the heating to welding temperaturealong on the very surfaces of such bands, the metal inwardly of suchsurfaces will receive substantially less heat and remain relativelyrigid permitting a good forged weld under pressure between the surfacebands which are heated to welding temperature.

With the embodiments of all of the figures it will or dinarily benecessary to provide for fluid cooling of the electrode supports. Thismay be readily accomplished by providing conduits, as at 36, 37, forcooling fluids such as, for example, water as is best shown in Fig. 2,these conduits being connected respectively to suitable circulatingcavities as at 38, 39 formed in the electrode supports. These coolingfluid connections are further indicated as will be apparent in Figs. 1and 4.

The use of the above-described sliding contacts in combination with theuse of high frequency current is particularly desirable as compared withthe use of low frequency current with roller contacts as sometimesheretofore proposed for some welding operations. This is true becausewith such sliding contacts and high frequency current an extendedcontact area may be achieved and it is unnecessary that the contacts beapplied under any considerable pressure since the high frequency currentwill flow into the metal edges with such contacts with out the danger ofany arcing at the contacts and consequent difficulties and the flow willbe closely defined to the edges where needed. Furthermore, since rollercontacts would touch the edges only tangentially with substantially onlya line contact, such rollers, particularly with low frequency currents,are not capable of conducting such current into the edges effectivelyand without prohibitive arcing unless subjected to great pressure whichwould tend to distort or crush the metal strip and such roller contactsif large enough to be effective with their pressure applying means wouldbe difficult to mount and support within the limited space available atthe approaching gap edges in the making of helically wound tubing. Andfurthermore, low frequency current will tend to distribute itself widelyaway from the gap edges and thus be largely wasted.

With above of the above-described modifications, if desired, the annulargap in the mandrel,- such as indicated at 23 by dotted lines, may befilled by any suitably known good heat resistant material therebyforming a firm support for the edges being welded at the weld point andavoiding the conduction of current into the metal of the mandrel. Insome cases, particularly where a thin walltubing is being formed, themandrel may be formed entirely of insulating means or covered with atubing of insulation. 7

Although certain particular embodiments of the inven- ,various furthermodifications thereof, after study of this specification, will beapparent to those skilled in the art io'which the invention-pertains;Reference should; accordingly be had to the appended claims indetermining the scope of the invention.

What is claimed and desired to be secured by Letters Patent is:

1. In a method for forming metal tubing by helically winding a metalribbon to form successive convolutions joined together at their edges bya helical butt-welded seam, the combination of steps which comprises:advancing the ribbon generally tangentially and fiatwise onto a mandrelwith the edges of the ribbon positioned at an angle to the axis ofthemandrel corresponding to the pitch of the desired helically welded seam;forming the ribbon into a succession of convolutions with abutting edgesand embracing the mandrel while advancing said convolutionslongitudinally along on the mandrel; welding at a substantially fixedweld point the trailing edge of each convolution to the forward edge ofthe ribbon substantially as the ribbon starts to form into a convolutionabout the mandrel, by applying contacts respectively to the edges whichare to be welded together shortly in advance of said weld point, saidcontacts respectively being connected to the terminals of a source ofcurrent of the frequency of 100,000 cycles per second or higher, wherebysaid current flows from said contacts along said edges to and fromsubstantially the weld point, the resulting resistance heating of suchedges being substantially concentrated along such edges and acting toincrease the temperature thereof until same come into contact adjacentthe weld point and whereby said forward edge of the ribbon then wipesacross said trailing edge into its final butt-welded position in respectthereto; and applying pressure to said ribbon in a directionlongitudinally of the mandrel means for forcing the forward edge thereofunder pressure against said trailing edge at the weld point.

2. In a method for forming metal tubing by helically winding a metalribbon to form successive convolutions joined together at their edges bya helically welded seam, the combination of steps which comprises:advancing the ribbon generally tangentially and flatwise onto a mandrelwith the edges of the ribbon positioned at an angle to the axis of themandrel corresponding to the pitch of the desired helically welded seam;forming the ribbon into a succession of convolutions embracing themandrel while advancing said convolutions longitudinally along on themandrel; welding at a substantially fixed weld point the trailing edgeof each convolution to the forward edge of the succeeding convolution byapplying contacts respectively to the edges which are to be weldedtogether, shortly in advance of said weld point, said contactsrespectively being connected to the terminals of a source of current ofa frequency of the order of 100,000 cycles per second or higher, wherebysaid current flows from said contacts along said edges to and fromsubstantially the weld point, the resulting resistance heating of saidedges being substantially concentrated along such edges and acting tocontinue to increase the temperature thereof until same come intocontact; applying pressure to the convolutions longitudinally of themandrel means for forcing said edges into welded engagement at the weldpoint; and maintaining the contact which engages said trailing edge at adistance from the weld point sufiiciently different from the distance ofthe other contact from the weld point, whereby opposed points of weldingon the two edges when they reach the weld point will be heatedapproximately to the same welding temperature notwithstandingdifferences in the rate of heating of said edges in travelling from thecontacts to the weld point.

3. In a method for forming metal tubing by helically winding a metalribbon to form successive convolutions joined together at their edges bya helical butt welded seam, the combination of steps which comprises:advancing the ribbon generally fiatwise and tangentially of aconvolution of the desired tubing with the edges of the ribbonpositioned at an. angle to the axis of the tubing being formed, suchangle corresponding to the pitch of the desired helically welded seam;forming the ribbon into a succession of convolutions with abutting edgeswhile advancing such convolutions longitudinally of said axis; weldingat a substantially fixed weld point the trailing edge of eachconvolution to the forward edge of the ribbon substantially as theribbon starts to form into a convolution, by applying contactsrespectively to the edges which are to be welded together shortly inadvance of said weld point, said contacts respectively being connectedto the terminals of a source of current of a frequency of the order of100,000 cycles per second or higher, whereby said current flows fromsaid contacts along on said edges to and from substantially the weldpoint, the resulting resistance heating of such edges beingsubstantially concentrated along on the edge surfaces and acting toincrease the temperature thereof until same come into contact adjacentthe weld point and whereby said forward edge of the ribbon then wipesacross said trailing edge into its final butt-welded position withrespect thereto; and applying pressure to said ribbon in a directionlongitudinally of said axis for forcing said forward edge under pressureagainst said trailing edge at the weld point.

4. In a method for forming metal tubing by helically winding a metalribbon to form successive convolutions joined together at their edges bya helically welded scam, the combination of steps which comprises:advancing the ribbon generally flatwise and tangentially of aconvolution of the desired tubing with the edges of the ribbonpositioned at an angle to the axis of the tubing being formed, suchangle corresponding to the pitch of the desired helically welded seam;forming the ribbon into a succession of convolutions while advancingsaid convolutions longitudinally of said axis; welding at asubstantially fixed weld point the trailing edge of each convolution tothe forward edge of the succeeding convolution by applying contactsrespectively to the edges which are to be welded together shortly inadvance of said weld point, said contacts respectively being connectedto the terminals of a source of current of a frequency of the order of100,000 cycles per second or higher, whereby said current flows fromsaid contacts along on said edges to and from substantially the weldpoint, the resulting resistance heating being substantially concentratedon facing portions along on said edges and acting to continue toincrease the temperature thereof until same come into contact; applyingpressure for forcing such heated edge portions into wording engagementat the weld point; and maintaining the contact which engages saidtrailing edge at a distance from the weld point sufficiently differentfrom the distance of the other contact from the weld point, wherebyopposed points of welding on the two edges when they reach the weldpoint will be heated approximately to the same welding temperaturenotwithstanding dilferences in the rate of heating of said edges intravelling from the contacts to the weld point.

5. In a method for forming metal tubing by helically winding a metalribbon to form successive convolutions joined together at their edges bya helically welded overlapping searn, the combination of steps whichcomprises: advancing the ribbon generally ilatwise and tangentially of aconvolution of the desired tubing with the edges of the ribbonpositioned at an angle to the axis of the tubing being formed, suchangle corresponding to the pitch of the desired helically welded seam;forming the ribbon into a succession of convolutions with a band portionon the forward edge of said ribbon facing and overlapping a band portionon the trailing edge of the adjacent convolution and while advancing theconvolutions longitudinally of the axis, welding said band portionstogether at substantially a fixed location by applying contactsrespectively to or adjacent said band portions shortly in advance ofsaid location, said contacts respectively being "7 connected to theterminals ofa source of current of a frequency of the order of 100,000cycles per second or higher, whereby said current flows from saidcontacts to and from the location of the weld point and is concen tratedbecause of its said frequency on the band surfaces, the width of thebands heated being determined by the extent of the overlap thereof, theresulting resistance heating 'of said band surfaces acting to continueto increase the temperature thereof until same come into con tact atwelding temperature substantially at said location; and applyingpressure to the overlapping portions after same come into contact, topress same into welded engagement;

6. In a method for forming metal tubing by helically winding a metalribbon to form successive convolutions joined together at their edges bya helically welded seam, the steps for butt welding uniformly andcontinuously the trailing edge of the convolutions to the opposed edgeof succeeding convolutions which comprises: forcing such edges togetherunder pressure substantially at a fixed weld point, the edges beingspaced apart in advance of such point; applying current of a frequencyof the order of 100,000 cycles per second or higher to flow from garagespoints at said edges respectively to and from the weld I point, theresulting resistance heating of such edges being substantiallyconcentrated along on such edges and acting to continue to increase thetemperature thereof until same come into contact at welding temperature,the convolutions as successively welded to form tubing being advancedlongitudinally of the axis of the tubing and the high frequency currentflows on such edges being in a direction at a substantial angletransversely of such advance.

France Dec. 15, 1954

